5-Aminotetrazoles, substituted, azides

Other approaches to tetrazoles were also recently published. Primary and secondary amines 195 were reacted with isothiocyanates to afford thioureas 196, which underwent mercury(II)-promoted attack of azide anion, to provide 5-aminotetrazoles 197 . A modified Ugi reaction of substituted methylisocyanoacetates 198, ketones, primary amines, and trimethylsilyldiazomethane afforded the one-pot solution phase preparation of fused tetrazole-ketopiperazines 200 via intermediate 199 <00TL8729>. Microwave-assisted preparation of aryl cyanides, prepared from aryl bromides 201, with sodium azide afforded aryl tetrazoles 202 . 

The imidoyl azide-tetrazole ring-chain isomerism of tetrazoles develops into a wide-ranging example of the Dimroth rearrangement in the thermal behavior of substituted 5-aminotetrazoles <84JHC627>. An example with 5-hydrazinotetrazoles is shown in Scheme 10 <88BSB543>. The reaction... 

Attempts to apply the azide-tetrazole isomerism to the synthesis of tetrazolo[l,5-a][l,3,5]triazines were published <88IZV491>. This equilibrium was found to be shifted generally to the ring opened azides (31), and the maximum amount of the tetrazole (32) of 15% was detected in DMSO-de at 20 °C in the case of = H, R = morpholino group. The same tetrazolo ring system was, however, found to be stable with 5-styryl and 7-thio substitution <87LA65> aminotetrazole (33) when reacted with cinnamoyl isothiocyanate alTorded the tetrazolotriazine-thione (34) most likely formed via cyclization of the intermediate thiourea. 

The syntheses of substituted 5-aminotetrazoles 228, using azide ions for assembling the tetrazole scaffold, can be divided into two different approaches. The first approach is the addition of sodium azide to car-bodiimides 222 [156,157] or cyanamides 223 [158-161]. The second approach is the nucleophilic substitution of a chlorine in a-chloroformamidines 224 [162], the nucleophilic substitution of benzotriazole in (benzotria-zolyl)carboximidamides 225 [163], the nucleophilic substitution of the sxflfite anion in aminoiminomethanesulfonic acids 226 [164] and the nucleophilic substitution of sulfur from thioureas 227 in the presence of mercury [165] or lead [ 166-169] salts in the presence of an azide ion (Scheme 43). In this chapter, the main focus is on the addition of azides to carbodiimides 222 to form substituted 5-aminotetrazoles 228. 

Scheme 43 Methods for the synthesis of substituted 5-aminotetrazoles 228 that involve azides [156-169]...

A useful method for the preparation of mono-, di- and trisubstituted 5-aminotetrazoles 253 starts from substituted thiourea 250 that is readily accessible by conversion of an amine 248 with an isothiocyanate 249. The thiourea 250 is reacted at room temperature with sodium azide in the presence of mercuric chloride in DMF with triethylamine as a base. In the initial step of the reaction, a mercury(II)-activated thiourea 251 is formed as an... 

Other Nucleophilic Substitution Reactions. Nucleophilic substitution of a variety of substituted aminoiminomethanesulfonic acids with cyanide leads to the corresponding aminoimi-noethanenltrlles in 30-87% yield. A number of substituted aminoiminomethanesulfonic acids react with sodium azide in acetic acid to give the corresponding 5-aminotetrazole. This reaction Is subject to pronounced steric hindrance. Hydroxyl-amine and cyanamlde also give nucleophilic substitution of the sulfonic acid group. ... 

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